An electron has a mass of $$9.1 \times 10^{-31} \mathrm{~kg}$$. It revolves round the nucleus in a circular orbit of radius $$0.529 \times 10^{-10} \mathrm{~m}$$ at a speed of $$2.2 \times 10^6 \mathrm{~ms}^{-1}$$. The magnitude of its angular momentum is

$$ \text { If the nuclear radius of }{ }^{27} \mathrm{Al} \text { is } 3.6 \text { fermi, the nuclear radius of }{ }^{125} \mathrm{Fe} \text { is } $$

A nucleus with mass number 190 initially at rest emits an alpha particle. If the $$\mathrm{Q}$$ value of the reaction is $$4.5 \mathrm{~MeV}$$, the kinetic energy of the alpha particle is

In a hydrogen atom, if electron is replaced by a particle which is 40 times heavier but has the same charge, then, the ratio of the radius of the first excited state of a normal hydrogen atom to the ground state of the above atom is